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published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

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No description available.

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2005. / School of Health Systems and Public Health (SHSPH) / Unrestricted

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The rapid rising anthropogenic emissions driven by economic growth over China documented by satellite observations and bottom-up inventories have led to severely degraded air quality, and also have been suggested to be linked to the recent upward trends of tropospheric O₃ over the regions downwind of China. Multi-scale modeling analyses facilitated by ground-level, aircraft and satellite observations have been conducted to understand the atmospheric chemistry over China. Analyses using a 1-D photochemical model constrained by measurements at Beijing in August of 2007 suggest that reactive aromatic VOCs are the major source (~75%) of peroxy acetyl nitrate (PAN). Detailed radical budget analyses reveal the very fast ROₓ (OH + HO₂ + RO₂) production, recycling and destruction driven by VOC oxidation and heterogeneous processes. Photoenhanced aerosol surface uptake of NO₂ is found to be the predominant source of nitrous acid (HONO) during daytime (~70%). 3-D regional modeling analyses of tropospheric vertical column densities of glyoxal (CHOCHO) from SCIAMACHY show that anthropogenic emissions of aromatic VOCs are substantially underestimated (by a factor of 5 - 6, regionally varied) over China. Such an underestimation is the main cause of a large missing source of CHOCHO over the region in current global models, and could also partly explain the underestimation of organic aerosols in previous modeling studies.

Building environmental conditions such as ventilation and contaminant concentrations are important factors that influence occupant health and comfort. The objective of the present work is to investigate how personal exposure to gaseous and particulate pollutants depends on indoor airflow, source characteristics, and occupant activity in commercial and residential environments. The study examines airflow and pollutant transport using experimental measurements in conjunction with computational fluid dynamics (CFD). The results demonstrate that breathing has a measurable influence on the airflow in an occupant breathing zone, but it has very small impacts on the occupant thermal plume. The results also show that breathing can significantly affect inhaled particle concentrations, even though the influence varies with source position and particle size. Also, localized hand motions of a sitting manikin do not significantly disrupt the upward thermal plume. In typical US residences, forced convection driven mixing airflow or buoyancy driven stratified airflow occurs depending on the HVAC fan operation (fan on or fan off, respectively). The measured transition period between mixing flow (fan on) and stratified flow (fan off) is approximately one minute, implying that most airflow in the residence is either dominated by mixing or stratification. A high level of exposure to short-term pollutant sources, such as resuspension of particles from floor surfaces due to human activity, more likely occurs with stratified flow than with highly mixed airflow. This is due to the strong influence of the occupant thermal plume that transports the pollutants into the breathing zone. Furthermore, by transporting air containing ozone across the reactive occupant surface, the occupant thermal plume has a large effect on exposure to ozone reaction products. Due to the reaction of ozone with the skin oils and clothing surfaces, the occupant surface boundary layer becomes depleted of ozone and conversely enriched with ozone reaction products. The parameter ventilation effectiveness quantifies the effectiveness of airflow distribution and can be used for assessment of exposure to gaseous pollutants. Based on the study results, the usefulness of ventilation effectiveness as an indicator of exposure to particulate pollutants depends on the particle size. For small particles (~1 [mu]m), an increase of ventilation effectives caused a decrease in occupant exposure, while for large particles (~7 [mu]m), source location and airflow around the pollutant source are significant factors for the exposure, and the ventilation effectiveness has very little to no effect. / text

An online, semi-continuous instrument to measure both total and gas phase atmospheric reactive oxygen species (ROS) and determine the concentration of ROS in the particle phase (ROS(p)) was developed. This instrument was based on a fluorescent probe for quantifying ambient ROS, specifically 2'7'-dichlorodihydrofluorescin, or DCFH probe. This probe was analyzed for sensitivity to a variety of offline and online parameters for efficient use in a field instrument. The ROS(p) instrument measures the peak light intensity at 530 nm to determine ambient ROS concentrations. ROS particles and gases are collected in a mist chamber in a nebulized mist. The instrument alternates measurements of ROS(p+g), or ROS(tot) by means of an inline filter. Fine (PM₂.₅) (ROS(p) is determined by subtraction of the ROS(g) concentration from the ROS(tot), as the ROS(g) signal could not be excluded. This instrument was tested during the summer (May-July) of 2012 at urban and rural sites in the metropolitan Atlanta and surrounding region. Concentrations of ROS(p) determined from this instrument were often below limit of detection. Average concentrations of ROS(p) were found to be 0.25 nmol/m³ in urban Atlanta (Jefferson St. and Georgia Tech), and 0.15 nmol/m³ in Yorkville, a rural site. A side by side comparison of this method with a filter collection method was made in July. The average ROS(p) offline concentrations were 0.15 nmol/m³. These concentrations were comparable to the online average concentrations of 0.21 nmol/m³ for the same period of time. This average and the majority of the measurements comprising it is dominated by the high limit of detection. The ROS instrument as constructed and operated is an efficient way to conduct ROS(p) measurements at the level of a filter study while reducing the labor intensive filter collection and extraction. In order for this instrument to be successful at measuring ambient ROS in the particle phase, the removal of the gas phase from the current sampling scheme is critical as the ROS(g) concentrations are over 90% of the measured ROS. The system as currently operable is best suited for source measurements, including biomass burning plumes or fresh exhaust to capture immediate formation.

Experiments were conducted to determine the photocatalytic degradation of three types of gas-phase compounds, NOX, VOCs, and chloramines, by TiO2 impregnated tiles. The oxides of nitrogen NO and NO2 (NOx) have a variety of negative impacts on human and environmental health ranging from serving as key precursors for the respiratory irritant ozone, to forming nitric acid, which is a primary component of acid rain. A flow tube reactor was designed for the experiments that allowed the UV illumination of the tiles under exposure to both NO and NO2 concentrations in simulated ambient air. The reactor was also used to assess NOx degradation for sampled ambient air. The PV values for NO and NO2 were 0.016 cm s-1 and 0.0015 cm s-1, respectively. For ambient experiments a decrease in ambient NOx of ~ 40% was observed over a period of roughly 5 days. The mean PV for NOx for ambient air was 0.016 cm s-1 and the maximum PV was .038 cm s-1. Overall, the results indicate that laboratory conditions generally simulate the efficiency of removing NOx by TiO2 impregnated tiles. Volatile organic compounds (VOC's) are formed in a variety of indoor environments, and can lead to respiratory problems (US EPA, 2010). The experiments determined the photocatalytic degradation of formaldehyde and methanol, two common VOCs, by TiO2 impregnated tiles. The same flow tube reactor used for the previous NOX experiments was used to test a standardized gas-phase concentration of formaldehyde and methanol. The extended UV illumination of the tiles resulted in a 50 % reduction in formaldehyde, and a 68% reduction in methanol. The deposition velocities (or the photocatalytic velocities, PV) were estimated for both VOC's. The PV for formaldehyde was 0.021 cm s-1, and the PV for methanol was 0.026 cm s-1. These PV values are slightly higher than the mean value determined for NO from the previous experiments which was 0.016 cm s-1. The results suggest that the TiO2 tiles could effectively reduce specific VOC levels in indoor environments. Chlorination is a widespread form of water disinfection. However, chlorine can produce unwanted disinfection byproducts when chlorine reacts with nitrogen containing compounds or other organics. The reaction of chlorine with ammonia produces one of three chloramines, (mono-, di-, and tri-chloramine). The production of chloramines compounds in indoor areas increases the likelihood of asthma in pool professionals, competitive swimmers, and children that frequently bath in indoor chlorinated swimming pools (Jacobs, 2007; Nemery, 2002; Zwiener, 2007). A modified flow tube reactor in conjunction with a standardized solution of monochloramine, NH2Cl, determined the photocatalytic reactions over the TiO2 tiles and seven concrete samples. The concrete samples included five different concrete types, and contained either 5 % or 15 % TiO2 by weight. The PV for the tiles was 0.045 cm s-1 for the tiles manufactured by TOTO Inc. The highest PV from the concrete samples was 0.054 cm s-1. Overall the commercial tiles were most efficient at reducing NH2Cl, compared to NOX and VOC compounds. However, the concrete samples had an even higher PV for NH2Cl than the tiles. The reason for this is unknown; however, distinct surface characteristics and a higher concentration of TiO2 in the concrete may have contributed to these findings.